A meta-analysis of 8 breast cancer adjuvant therapy trials from the l97Os has suggested that adjuvant oophorectomy may be associated with long-term increases in disease-free and overall survival. Essentially all breast cancer adjuvant trials of all types have been conducted with populations in Western or developed countries and most have not standardized treatment on relapse, which makes interpretation of overall survival results difficult. Concerns about severe menopausal symptoms and about long-term adverse effects of oophorectomy on the cardiovascular system and skeleton, have prevented initiation of new adjuvant oophorectomy studies. The addition of tamoxifen following oophorectomy is suggested by recent data demonstrating that tamoxifen has estrogen-like favorable effects on cardiovascular risk factors and on bone density. A premenopausal population with a lower estrogen profile such as is observed in Asian women might be expected to derive the greatest net benefit from an oophorectomy/tamoxifen adjuvant regimen. Breast cancer is the most common malignancy in women in northern Vietnam and the second most common cancer in the south. In Vietnam, financial and other resources for treatment are limited, and the standard of care for operable breast cancer throughout Vietnam is observation after surgical +/-radiotherapy treatment. The investigators have begun a randomized controlled trial of surgical oophorectomy and tamoxifen versus this treatment on first recurrence for premenopausal Vietnamese women with TNM Stage II-IIIA carcinoma of the breast. Three and five year overall and disease-free survival are the study endpoints; the accrual goal is 600 women over 3 years. This study plan provides 80-90% power for overall survival at 3 years, and 70-80% power at 5 years. One-hundred and forty- two women have entered the study in 15 months and detailed symptom reports in the first 121 women followed have indicated acceptable vasomotor toxicity. Several histopathologic prognostic factors will be investigated and used in the survival analysis including immunohistochemically determined estrogen add progesterone receptor protein content. The investigators have functional systems in place to conduct this trial to a successful conclusion yielding direct information on the impact of adjuvant oophorectomy and tamoxifen in Vietnamese women. These results will have important implications for adjuvant therapy given to women with breast cancer in Asia in particular, but also worldwide and in the United States. Support is requested only for the American operations component of this trial.